1. Field of the Invention
The present invention relates to a waterdrop-proof camera and, more particularly, to a waterdrop-proof camera being waterproof enough to enable it to be used even in a rainfall.
2. Description of the Related Art
When a zoom lens barrel is moved backward and forward during zooming or the like, the internal pressure of the camera changes. Therefore, for camera with zoom lenses to be waterproof, it must be constructed so as to absorb such a changes in the internal pressure of the camera. A camera constructed in the above way has already been disclosed for example, U.S. Pat. No. 4,931,816 or Japanese Laid-Open Utility Model Application Sho/63-113137.
The camera disclosed in U.S. Pat. No. 4,931,816 has an air circulation passage which enables the inside of the camera to communicate with the outside thereof, the inside of which passage has a water-repellent fine porous member arranged therein. Thus, air is circulated through the passage by means of the water-repellent fine porous member, thus preventing water from passing through the passage. This camera is a complete waterproof camera which prevents water immersion and it is pre-supposed that special members known by the trade names of "Gore-Tex" by Japan Gore-Tex Inc., "Entrant" by Toray Industries, Inc., Japan, "Micro-Tex" by Nitto Denko Co., Ltd., Japan, are used for the water-repellent fine porous member.
The camera disclosed in Japanese Laid-Open Utility Model Application Sho/63-113137, unlike that of U.S. Pat. No. 4,931,816, is a waterproof camera which can be used in daily life, that is, a waterdrop-proof camera waterproof enough to enable it to be used even in a rainfall. However, the construction thereof is substantially the same as that of U.S. Pat. No. 4,931,816. A member for sealing up vent holes comprises a filter which is not water permeable and is air permeable and formed of a porous ethylene tetrafluoride resin known by the trade name of "Gore-Tex".
In the above-described waterproof and waterdrop-proof technology of the prior art, making the camera waterproof of and adjusting the change in the atmospheric pressure, between the inside and the outside of the camera are performed by a member having a great number of holes whose respective diameters are smaller than those of water droplets (100 .mu.m to 300 .mu.m) and larger than water vapor (0.0004 .mu.m).
Such members can be made considerably waterproof, but they are not very air permeable. Therefore, when such members are used for the purpose of making a camera waterproof and air permeable, it takes a sufficient amount of time to adjust the difference between the atmospheric pressure of the the inside and that of the outside of the camera. That is, a zooming operation must be performed quite slowly. In addition, a zooming load increases because of insufficient air permeability, causing a great amount of load on a motor for performing zooming and a speed-reduction gear system. As a consequence, a powerful zooming motor and a strong gear and gear shafts are required. As a result, problems arise, for example, costs increase, and a large construction is required, and thus miniaturization of camera is hindered.
However, the above-mentioned waterproof and air permeable member has a problem in that since it is provided with fine holes, if a user touches it inadvertently, it may be clogged, thus deteriorating the air permeability. Therefore, such member must be arranged in a place in camera where usually a user cannot touch the member when holding the camera, causing drawbacks, for example, design possibilities are limited and costs are high because of the specialized nature of the member.